Sectional digital switch



May 14, 1963 H. D. WRIGHT 3,089,923

SECTIONAL DIGITAL SWITCH Filed June 15, 1959 2 Sheets-Sheet 2 INVENTOR.leer DUQLE) IMP/6N7 rraeA/EK United States Patent Ce 3,089,923 SECTIONALDIGITAL SWITCH Harry Dudley Wright, Pasadena, Calif., assignor toEndevco Corporation, Pasadena, Calif., a corporation of California FiledJune 15, 1959, Ser. No. szasas 11 Claims. (Cl. 200-) This inventionrelates to digital switching devices which may be constructed as aplurality of assembled units that are manually actuable to operateelectrical switching means in each unit for feeding the results intoappropriate electronic instruments for whatever purpose required.

An important object of this invention is to provide a novel digitalswitching unit, by means of which .a plurality of substantiallyidentical such units may be arranged in a compact in-line series toprovide for counting to as high a number as may be desired.

Another object of the invention is to provide an efiicient digitalswitching unit, especially one containing electrical switching means,which is easily duplicated for assembling into a multiple in-lineswitching system to whatever extent needed for any given purpose.

A still further object of the invention is to provide a digitalswitching unit embodying a finger-operated wheel positioned to beengaged by an operators finger for positivc movement of the wheel, onestep at a time or two steps at a time, to advance the wheel for bringinginto viewing position digits delineated thereon, such digits beingsuccessively advanced by the operator.

A still further object is to provide the wheel of such a switching unitwith notches which are employed to advance the wheel from one positionto another and which also cooperate with a spring to set and retain thewheel in a predetermined position.

A still further object of the invention is to provide means in such aswitching unit for positively limiting movement of the operators fingerto one digit spacing at a single operation.

A still further object of the invention is to provide means in such aswitching unit for readily setting the wheel in a predetermined positionas the operators finger is withdrawn after operating the switching unit.

An additional object of the invention is to provide, in conjunction witha rotary switching wheel in each unit, an electrical switching devicefor completing electrical circuits as the respective wheels are rotateddigit by digit, whereby to conduct electrical currents through suchcompleted circuits to an instrument into which they are to be fed.

It is a still further object to provide a switching unit of theindicated character having a casing providing means for rotatablymounting a switching wheel in the casing, the casings being so arrangedthat a series of such casings are alignable to mount their respectiveswitching wheels and also the opposite sides of the adjacent switchingwheels in an aligned assembly.

Other objects of the invention, and various features of constructionthereof, will be apparent to those skilled in this art, upon referenceto the following specification and the accompanying drawings whereincertain embodiments are disclosed to indicate what is presently deemedto be the best manner of constructing and employing the invention.

In these drawings:

FIGURE 1 is a face view of a multiple switching system of this inventionmade up of three aligned switching units and two end plates assembledtherewith;

FIG. 2 is a cross-section taken from the line 22 of P16. 1 on anenlarged scale;

FIG. 3 is a similar cross-section taken from the line 3--3 of FIG. 1;

3,98%,923 Patented May 14, 1963 FIG. 4 is a transverse cross-sectiontaken from the line 4-4 of FIG. 2;

FIG. 5 is a detail showing of a Wiper switch;

FIG. 6 is a view similar to that of FIG. 2, but showing switchingmechanism employing a binary system as distinguished from the decimalsystem of FIGS. 2 to 5;

FIG. 7 is a cross-section corresponding with that of FIG. 3, butillustrating the binary system switching mechanism of FIG. 6; and

FIG. 8 is a detail of the wiper switch of FIGS. 6 and 7.

As indicated in FIG. 1, three casing units 10, which are substantiallyidentical in construction, are shown as being assembled for the purposeof performing in-line counting operations up to 999. At each end or" theassembly of the three casing units 19, there is provided an aligned endplate 12 retained in assembled position by the same means which retainthe casing units '10 in assembled position, as more fully describedhereinafter.

The casing 10 in each unit, as the assembly of FIG. 1 is viewed inelevation, includes a top wall 14 (FIGS. 2 and 3) which is relativelynarrow as compared with its length, a front wall in the form of twospaced wall sections 15, and a bottom wall 16, these having the samenarrow configuration as the top wall 14. In addition, each casing unitIt) has a back wall 18 as seen in FIG. 2, which is somewhat narrowerthan the walls 14, 15, and 16, to provide a narrow slot-like space forthe reception between the walls 14 and 16 of a projecting rearward endof a circuit board 20, as presently to be more fully described.Additionally, each casing unit 1% is provided at one side with a sidewall 22. All of the described wall portions may be integral with oneanother, as conveniently provided by a molded thermo-setting plasticconstruction. As seen at the right of FIG. 2, the end of the circuitboard 20 projecting beyond the back wall 18 is that of the circuit boardof the unit 10 lying immediately behind the walls 18 and 22 shown inelevation. Each end plate 12 is desirably .stamped from sheet metal toprovide a side closure plate 23 and an integral right-angularly disposedflange 24, as presently more fully described.

The spaced portions 15 of the forward wall of each casing 10 provide agenerally rectangular open window 25 between them, which window is thewidth of the wall sections 15 and the upper and lower walls 14 and 16.In addition, the upper edge of the side wall 22 is provided with alaterally outward-1y directed and somewhat elongated lip 26, whichoverhangs the circuit board 20 of the adjacent casing unit and which, asseen in FIG. 1, is at the left of its window 25. Additionally, eachelongated lip 26 is provided at its opposite ends with short inwardlyoverhanging flanges or lips 27, the elongated lip 26 and the short lips27 cooperating among them to define an inner window 28 for viewing adigit presented on a switching wheel 30.

Each switching wheel 39 includes a body portion or hub section 32 fromwhich extends outwardly a radially directed circumferential fingerflange 33, which is arcuate- 1y notched at 34 to provide curved fingerlugs 35 for rotating the wheel. The finger flange 35 lies at one side ofits Wheel 39, and at the opposite side of wheel there is provided acylindrical rim 36, which carries a series of ten digits, 0 to 9 of thedecimal system, as indicated in FIG. 1, these digits lying alongside thefinger lugs 35, of which there are also ten in number. This rim 36rotates beneath the small inwardly overhanging flanges 27 so that, aseach digit is moved into position, it is viewed through the small window28 provided between the small overhanging fianges 27 and between theelongated outwardly overhanging flange 26 and the finger flange 33 andits lugs the finger flange 33 thus exaosasas tends outwardly alongsidethe overhanging window-forming flanges 27 and rotates adjacent the sideedges thereof.

The hub or body portion 32 of each switching wheel 3% is centrallyprovided at its opposite sides with pivots 38, which may be integralwith the wheel 3%, especially where the entire wheel is cast or ismolded from thermosetting plastic or the like. These pivots 38 may bejournaled in bores providing bearings, such as a bore in an adjacentboss 49 in each side wall 22 and a bore in an appropriate bearing 41provided in each circuit board 2% as best illustrated in FIG. 4.

Each circuit board is secured in place by means of screws 42, which arethreaded into appropriate cast bosses at the corners of the respectivecasing units it). Additionally, the circuit boards 29 may be bound inplace by means of through bolts 44 which extend entirely through theassemblage of the several casing units it and the end plates 12 seen inFIGS. 1 and 4, these bolts 44 being positioned in bores in appropriatecorner bosses of the casing units as illustrated in FIGS. 2, 3, and 4.

By the indicated mounting of the various switching wheels 39, the lattermay be readily rotated to advance the various digits into the viewingpositions indicated in FIG. 1, the operators finger being disposed in anotch 34 and drawn forward against a finger lug 35 until his fingerengages the nearer front Wall portion or section 15, whereupon therotary movement of the wheel 32 ceases. These wall sections thus act asfinger stops or finger guides.

In cross-section, the notches 34 form arcs of about 100 to 140. Thesurfaces 15a of the front walls slope in directions that extend alongthe ends of the notch arcs at both ends of the window 25, being abouttangential to the ends of the arcs. With this arrangement, as theoperators finger moves the wheel from one position to another, thenotches and the digit to be viewed are registered accurately in thewindow as the finger is withdrawn, and then the wheel is held by virtueof the friction produced by the force between the switch contacts.

For the purpose of securing centering of a finger lug 35 in the positionto which the corresponding wheel 39 has been rotated, a centering spring45 is provided within and at the back of each casing unit 18. One end ofthe spring is shaped to fit into slots provided between a boss 4-6 thatreceives one of the screws 42 and the adjacent bottom wall 16 and partof the spring engages the adjacent rear wall 18 of the correspondingcasing unit 10 in order to anchor the spring in place. Such slots areindicated at 48 in FIG. 2, which also shows an offset retention finger45a at the fixed extremity of the spring 45 to insure proper springposition. The other end of the spring 45 is movable and is shaped to-match the curvature of the finger notches 34. Thus,

when a switching wheel 3% has been rotated by the operators finger tobring a digit into viewing position in the center of the small viewingwindow 23, and the operators finger has engaged against a finger stopwall section 15 as indicated in FIG. 2, the curved free extremity of thespring 45 settles down into a corresponding finger notch 34 and retainsthe respective wheel 3% in the new position. For some uses, the spring45 might be omitted. In such case, friction between various members isrelied upon to retain the switching wheel in place. However, the use ofthe spring 45 is better, since it provides a more positive holdingaction, especially when the unit is subjected to vibration or shockforces. In prior devices, stifi springs have been used for registeringrotatable wheels in desired positions. But, since registration isaccomplished in this invention as a result of the shapes of the windowedges in relation to the shapes of the notches, a soft spring may beemployed, since their sole function is to retain the wheel in position,not to force it into position.

It will be noted, also, that the notches 34 and finger lugs 35 of thewheels 30 are adapted to rotation of the wheels two steps at a time, asby two increments of motion through the action of the thumb. Asindicated in phantom in FIG. 6, the ball of the thumb first operatesagainst one lug 35 to move a wheel 36 one step forward and the distalend of the thumb then operates against the next lug 35 to move the wheela second step forward. Further, in view of the symmetrical constructionof the lugs 35 of each wheel 30, the wheels may be rotated in theopposite direction if desired for any reason, the end of the operatorsfinger pushing against the exposed lugs 35.

In connection with the assembling of a plurality of easing units It} andend plates 12 into a complete assemblage such as shown in PEG. 1, thelip 26, which overhangs the outside of each casing unit 1 (to the leftas viewed in FIG. 1) and which is integrally positioned at the top ofthe corresponding side Wall 22, is arranged so as to interlock at itsends under the inclined or beveled edges 5% of the two finger-stop wallportions 15 shown in FIGS. 2 and 3. For this purpose, the length of theoverhanging fian-ge 27 in each instance is slightly greater than thelength of the window opening 25 between the finger-stop wall portions15; this is best indicated at the left of FIG. 1. Thus, when one unit itis being assembled alongside an adjacent unit, such extending lipportions, indicated at 52 in FIG. I, lock under the beveled edges 56 ofthe adjacent stop portions 15. Such arrangement also helps maintain theinterior of the assembly dust-free.

For the purpose of accommodating an overhanging lip 26 in an end plate12 as seen at the left of FIG. 1, the latter is correspondingly slottedat 5 5 to receive the lip 26. Such a slot 54 is also seen at the rightof FIG. 1 in the other end plate 12. Each slot 5 exposes thecorresponding upper edge portion of the main plate or side wall 23 ofthe respective end plate 12. in order to cover the'slot 5d of the endplate 12 seen at the right of PEG. 1, and also to conceal the upper edgeof the corresponding circuit board 29 and the adjacent side wall 23 whenthe assembiy is completed, the flange 24 of this right end plate 12 isdesirably covered with a thin, stiff finish layer 55, which may be ofheavy metal foil, and which is shown as approximately half broken away.This layer 55 is provided with an overhanging extension tongue 55acorresponding in size with the lips 2-5 or" the casing units it toartialh enter the lar er window b and overhang the adjacent circuitboard 2%). In addition to serving as a closure plate or finish layer,the member 55 may at the same time be a name plate. It is secured inposition as by means of screws 55 received in screw holes 5% in the endplate flange 24, and said screws 5'5 are desirably employed to mount theassembly in the custorners apparatus for which this switching mechanismhas been developed.

The function of switching wheels is to make and break circuitscorresponding with the digits on the respective cylindrical rims 36, andthis is accomplished through the medium of the mentioned circuit boards22 and rotary wiper switches at concentrically mounted about the axes ofthe switching wheels 3% in position to make and break circuits by meansof contact members on respective circuit boards 26.

Each circuit board 2% receives and centers one of the pivot shafts 38,and the board carries so-called printed circuits, which include thecontacts to be engaged by the rotary wiper switches 60. Adjacent therespective axis or pivot shaft 38, each board 20 carries a printedcontinuous wiper ring or slip ring 62, and concentric therewith outsidethe wiper ring or slip ring 62, there is provided a circular series ofprinted contact segments 64 spaced from each other and constituting acommutator ring and corresponding with the ten digits on the rim 36 ofthe respective switching wheel 3%. Printed leads 65 extend from thevarious contacts or ring segments 64 to appropriate terminals 66 at theprojecting end of the respective circuit board 20 where they may bewired into any instrument with which the present digital switch is to beused. Some of the leads 65 are disposed on one side of the board 20,which is formed of insulating material, and some of them are provided onthe other side, appropriate through-connections, such as indicated at67, extending through the board from some of the contact segments 64 andthe respective lead 65 on the other side.

As shown in FIGS. 2, 3, and 4, the decimal system is employed, andmake-and-break fingers of each wiper switch 60 are positioned to contactsuccessively the commutator segments or contacts 64 on the circuit board20 as respective switching wheel 36 is rotated. Each wiper switch 60 hasa central ring member 70 (FIG. 5) secured in any suitable manner as at70a to the hub of respective switching wheel 39, and this ring member isin general positioned inside the locus of the slip ring 62, as well asinside the locus of the outer series of commutator segments or contacts64. To the inner ring or" each wiper switch 60, there are connected twowiper fingers 72 having contacting wiper terminals 74 (FIGS. 2 and S) toengage the slip ring 62. Also connected to the inner ring of each wiperswitch 60 is a pair of wiper fingers 75 having wiper terminals 76disposed at the locus of the circular series of contacts 64 on thecircuit board 2%. These wiper terminals 76 may be spaced either toconstitute the non-shorting break-before-make type of switchingmechanism, or they may be more widely spaced to provide the shorting ormake-before-break type of switching mechanism, according to therequirements of the circuits being switched.

With the mechanism thus described, as any one of the switching wheels 36is rotated step-by-step to present digits thereon successively to therespective windows 23, circuits are completed through the respectivecircuit boards, contacts thereon and the wiping fingers 72 and 75' ofthe respective wiper switch 66. The corresponding impulses are thentransferred from the terminal 66 to the customers instruments with whichthe present improvement has been connected by appropriate wiring.

The electrical arrangement illustrated in F168. 2, 3, 4, and 5, as hasbeen previously indicated, is for use with a decimal electrical system.The present structure, however, lends itself readily to the employmentof contact boards 20 and wiper switches 80 for use with binaryelectrical systems, and such an arrangement is illustrated in FIGS. 6,7, and 3, where the same casing units 10 and switching wheels 3i), withfinger lugs 35, are employed as with the decimal arrangement of FIGS. 1to 5.

Instead of employing the decimal contact arrangement represented in thestructure of FIGS. 1 to 5, a binary contact arrangement may also beemployed, such as that represented in FIGS. 6, 7, and 8. in the switchillustrated in those figures, a decimal or scale-of-ten switching wheel30 is employed, but the circular series of ten stationary contactsegments 64 of the contact arrangement of FIGS. 1 to 5 is replaced by aplurality of concentric annular zones in order to provide a switchingarrangement operating on a binary or scale-of-two basis. Also in thiscase, a five fingered wiper switch Si is employed in place of the wiperswitch 60.

The wiper switch '80 includes four contact fingers 1'95, 106, 107, and108, which are radially aligned, as well as an additional contact finger102. The area of the contact board 20 through which the various contactsof the wiper switch 80' move is divided into ten 36 consecutive sectorsS S S Both the numbers of the digits indicated by any switching wheeland the numbers of the sectors, increase in a counter-clockwisedirection about the shaft 38. In this arrangement, five zonal contactsare employed. The inner contact 82 constitutes a slip ring which isengaged by the contact 102. The outer contact 84 is provided with fiveuniformly spaced inwardly projecting extension segments 85 that lie insectors S S S S7, and S A short zonal segment 36 extends over sectors Sand S at the radius of the contact finger 106. A longer zonal segment 87occupies sectors S S S and S at the radius of the wiper finger 1437. Andtwo spaced electrically connected segments 88 and 3a occupy sectors S SS and S at the radius of the contact finger 108. With this arrangement,a coded binary output may be provided.

As illustrated in FIG. 7, the outer contact 84, together with itssegments 85, are connected by a suitable printed circuit lead toterminal 94. Likewise, the contact 86 is connected by a suitable printedcircuit lead to terminal 96. Similarly, the contact 87 is connected by asuitable printed circuit lead to terminal 97. And similarly the twocontact segments 38 and 88a are connected by a common printed circuitlead to each other and to a terminal 93. And the slip ring 82 isconnected by a suitable printed circuit lead to terminal 92. The fiveterminals 2, 94, 96, 97, and 98 are arranged at the rear edge of thecontact board 20 at the rear of the casing unit 10 to facilitateinsertion of the unit into and removal from a suitable electricalcontact plug.

With the above described arrangement of the segment 84 and its segments85, 86, 87, 88, and 83a operating in conjunction with the wiper switchand its various contact fingers M2, N5, 106, 107, and 193, anappropriate binary code is readily followed and the present digitalswitching system readily employed in conjunction with apparatus designedfor use with such coded arrangement.

From these disclosures, it is apparent that the digital switching systemof this invention is readily applicable for employment with anyappropriate numbers system, whether the system be decimal, binary,octal, or other usable numbering system.

Although only two specific embodiments of the invention have beenillustrated and described, it will be obvious that the invention is notlimited thereto, but is capable of being embodied in many other forms.Various changes which will suggest themselves to those skilled in theart may be made in the material, form, details of construction andarrangement of the elements Without departing from the scope of theinvention.

The invention claimed is:

1. A switch comprising an outer wall member of contoured configurationforming a limited switch actuation region disposed between and boundedby a pair of spaced, sloping and diverging outside surfaces, said pairof diverging surfaces extending outwardly from said switch actuationregion and being located adjacent opposite ends of said region, saidswitch actuation region having an open window including a portionextending substantially from one to the other of said sloping surfaces,a rotor mounted for rotation in either of two opposite directions on anaxis located anterior of said wall member and said open window portion,switching means coupled to said rotor for completing a plurality ofdiiferent electrical circuits in response respectively to movement ofsaid rotor to a plurality of predetermined different angular circuitregistration positions, said rotor comprising a movable operator portionhaving a plurality of spaced radial members at least one of which alwaysextends through said open window portion and each of which is adapted tobe manually engaged only in said limited switch actuation region of saidouter wall member, said radial members comprising lugs extendingoutwardly of said operator portion in sufficiently spaced relation toone another to permit insertion of a finger tip into the space at eitherside of each said lug between directly adjacent ones of said lugs topermit a turning force to be exerted upon said rotor in either of twoopposite directions by finger pressure exerted in a directionpredominantly circumferential and predominantly non-radial of saidrotor, one of said radial members comprising a lug disposed adjacent acentral part of said window portion at a given time and others of saidradial members comprising further lugs inclined to a,ose,ass

lie generally along both of said pair of sloping surfaces at said giventime, said sloping surfaces being respectively positioned to intercept afinger, engaging one or the opposite side respectively of said oneradial member, after said finger and said one radial member have movedsaid rotor in one or the opposite direction to bring said rotor into oneof said predetermined different circuit registration positions, therebyto cause switching to be effected in a succession of limited arcuaterotor rotations determined primarily by the positioning of said slopingsurfaces relative to the finger engaged one of said radial members.

2. The switch of claim 1 wherein said rotor further includes an indiciabearing section rotatable with said rotor, said window including afurther portion disposed adjacent said indicia bearing section andpositioned to permit the viewing of one indicium only on said indicabearing section at any given time.

3. The switch of claim 2 wherein said further window portion is disposedadjacent to and at one side of said first mentioned window portion, saidfurther portion being shorter in length than said first portion, theadjacent sides of said window portions merging with and opening into oneanother whereby said window is substantially T- shaped in configuration.

4. The switch of claim 1 wherein said switching means includes a printedcircuit disposed at a position anterior of said wall member, and wipermeans engaging said printed circuit, said wiper means and said printedcircuit being relatively rotatable for effecting a switching operationupon rotation of said rotor.

5. The switch of claim 4 wherein said printed circuit is carried by asupporting member fixed in position relative to said wall member, saidprinted circuit including arcuate conductive segments disposed atdifierent radial positions relative to said rotor axis of rotation, saidwiper means comprising a plurality of conductive fingers carried by saidrotor member at such diiierent radial positions, said rotor beingcontinuously rotatable through angles greater than 360 in each of saidopposite directions.

6. The switch of claim 1 including resilient detent means engaging aportion of said rotor for resiliently holding said rotor in its saiddifferent registration positions.

7. In a digital switching system:

a plurality of substantially identical units assembled side-by-side intoa compact digital switching assembly, each unit including:

a casing providing therewithin a mounting chamber,

a digit-carrying wheel rotatably mounted in said chamher,

said wheel having an interrupted circumferential finger flange providinga plurality of outstanding finger lugs and a plurality of finger notchesdisposed between said lugs, and said wheel having a digit-carrying rimat one side of said flange,

said casing having an outer face wall provided in its middie portionwith a view opening leaving a fingerstop portion of said face wall ateach end of said opening,

a peripheral portion of said finger flange projecting through saidopening and a peripheral portion of said rim projecting into saidopening between said finger-stop wall portions, whereby to present toview a selected member of a pluraiity of digits appearing around saidrim;

means extending through said units and binding them together, eachcasing having, at the side of its view opening opposite the fingerflange, a lip extending laterally a short distance toward the fingerflange of the adjacent casing and underlying portions of the finger-stopportions of the adjacent unit to assist maintenance of the assembly;

a circuit board mounted in each casing at the side thereof adjacent therespective finger flange and underlying the lip of the adjacent casing;

a wiper switch plate mounted about the axis or" each wheel and securedthereto on the side facing the adjacent circuit board, said switch plateand circuit board in each case having cooperating contacts; and

terminal means on each circuit board connected with the respectivecontacts.

8. A system as in claim 7, wherein each casing is open at one side andhas at its opposite side a side wall providing bearing means for therespective wheel, said side wall also providing bearing means for thewheel of an adjacent casing.

9. A system as in claim 8, wherein the respective circuit board isprovided with bearing means for the respective wheel.

10. A system as in claim 7, wherein each casing I a side wall providingbearing means for the respective wheel and the respective circuit boardhas bearing means for the respective wheel.

11. A system as in claim 7 wherein said finger notches correspond innumber to said finger lugs and are arcuate, and the digits on said rimcorrespond in number to said lugs, and said view opening defines a spacefor presenting to view simultaneously only one finger lug, two adjacentarcuate finger notches and a single digit of said wheel.

References Cited in the file of this patent UNITED STATES PATENTS1,555,969 Hatch Oct. 6, 1925 1,564,551 Gates Dec. 8, 1925 2,414,191 CoonJan. 14, 1947 2,421,881 Heasty June 10, 1947 2,662,949 Christensen Dec.15, 1953 2,824,191 Christensen Feb. 18, 1958 2,853,564 Gahgan Sept. 23,1958 2,874,338 Pease Feb. 17, 1959 2,967,917 Cole Jan. 10, 1961 FOREIGNPATENTS 760,989 France Mar. 7, 1934 440,222 Great Britain Dec. 23, 1935577,897 Great Britain June 5, 1946

7. IN A DIGITAL SWITCHING SYSTEM: A PLURALITY OF SUBSTANTIALLY IDENTICALUNITS ASSEMBLED SIDE-BY-SIDE INTO A COMPACT DIGITAL SWITCHING ASSEMBLY,EACH UNIT INCLUDING: A CASING PROVIDING THEREWITHIN A MOUNTING CHAMBER,A DIGIT-CARRYING WHEEL ROTATABLY MOUNTED IN SAID CHAMBER, SAID WHEELHAVING AN INTERRUPTED CIRCUMFERENTIAL FINGER FLANGE PROVIDING APLURALITY OF OUTSTANDING FINGER LUGS AND A PLURALITY OF FINGER NOTCHESDISPOSED BETWEEN SAID LUGS, AND SAID WHEEL HAVING A DIGIT-CARRYING RIMAT ONE SIDE OF SAID FLANGE, SAID CASING HAVING AN OUTER FACE WALLPROVIDED IN ITS MIDDLE PORTION WITH A VIEW OPENING LEAVING A FINGERSTOPPORTION OF SAID FACE WALL AT EACH END OF SAID OPENING, A PERIPHERALPORTION OF SAID FINGER FLANGE PROJECTING THROUGH SAID OPENING AND APERIPHERAL PORTION OF SAID RIM PROJECTING INTO SAID OPENING BETWEEN SAIDFINGER-STOP WALL PORTIONS, WHEREBY TO PRESENT TO VIEW A SELECTED MEMBEROF A PLURALITY OF DIGITS APPEARING AROUND SAID RIM; MEANS EXTENDINGTHROUGH SAID UNITS AND BINDING THEM TOGETHER, EACH CASING HAVING, AT THESIDE OF ITS VIEW OPENING OPPOSITE THE FINGER FLANGE, A LIP EXTENDINGLATERLLY A SHORT DISTANCE TOWARD THE FINGER FLANGE OF THE ADJACENTCASING AND UNDERLYING PORTIONS OF THE FINGER-STOP PORTIONS OF THEADJACENT UNIT TO ASSIST MAINTENANCE OF THE ASSEMBLT; A CIRCUIT BOARDMOUNTED IN EACH CASING AT THE SIDE THEREOF ADJACENT THE RESPECTIVEFINGER FLANGE AND UNDERLYING THE LIP OF THE ADJACENT CASING; A WIPERSWITCH PLATE MOUNTED ABOUT THE AXIS OF EACH WHEEL AND SECURED THERETO ONTHE SIDE FACING THE ADJACENT CIRCUIT BOARD, SAID SWITCH PLATE ANDCIRCUIT BOARD IN EACH CASE HAVING COOPERATING CONTACTS; AND TERMINALMEANS ON EACH CIRCUIT BOARD CONNECTED WITH THE RESPECTIVE CONTACTS.